Can low-carb diets make you cranky?

Which is better for weight loss -- a high-protein diet or a high-carb diet? That endless debate got a new twist this week.

In a yearlong study, Australian researchers found that both diets worked equally well when it came to shedding pounds, but those on the low-carb diet were in considerably worse moods.

The report, published in the Archives of Internal Medicine, assigned 106 overweight and obese men and women to either a low-carb diet high in fat and protein or a high-carb diet low in fat and protein.

The participants' weight was noted at weeks 8, 24, 40 and 52, and their emotional state was evaluated via three questionnaires measuring aspects of mood, including anxiety and depression.

Both groups lost an average of 30 pounds, slightly more than most studies of this type. And early on, both groups showed an improvement in mood.

However, although mood improvements remained in the high-carb group, they went back to original levels in the low-carb group.

Most studies on diets typically focus on pounds lost, pounds kept off and cardiovascular function. But there is good reason to also consider mood, said the study's lead author, Grant Brinkworth of the Commonwealth Scientific and Industrial Research Organisation-Food and Nutritional Sciences in Adelaide.

Dr. David Heber, director of the University of California, Los Angeles Center for Human Nutrition, said most people find diets to be stressful. "If you're going to feel crummy, there's no point in doing it," he said.

Exercise could be helpful here, Heber added.

"We can't just look at a diet," he said. "People can also use exercise as a mood elevator and stress reducer."

WHY SO GLUM?

The results could be evidence that it's tough to stick to a low-carb diet in cultures where high-carb foods are abundant, the authors speculated. The reason for the mood dip also could be biological -- a low-carb diet can cause a drop in levels of the brain chemical serotonin. Low serotonin levels are linked to depression.